The present invention relates to ascertaining defects in cylindrical objects such as tubes or pipes. More particularly, the invention relates to the testing of tubes, pipes or rods without rotating them but passing them past stationary transmitting and receiving equipment whereby tangentially produced azimuthal wave pulses are produced at a certain rate and received and the amplitudes are processed under formation of quotients for determining defects in the test object.
German printed patent application No. 26 05 405 discloses and suggests a method and equipment of the general type and variety to which the invention pertains and constituting the point of departure for further development. These kinds of equipment and types of methods are advantageous whereby specifically electrodynamic transducers are used for converting ultrasonic energy into electrical pulses and vice versa. These transducers will be arranged vis-a-vis the test object. The electrodynamic operation does not require any liquid coupling as is necessary in case of ultrasonic transducers. Also the rotation of the test object or of the equipment is to be avoided which is, from an equipment point of view, an advantage. However, it was found that this mode of processing the signals produced and generated by and in the equipment as well as by the test object are not reliable. It is to be observed that the ends (axial) of the test object do produce certain parasitic reflections and interferences which has some influence on the signals as they are received. These parasitic signals do not drop off in a monotonic function and are, therefore, no reliable indicator for the quality of the test object. Moreover, quotient formation of two amplitude maximum values as processed is rather sensitive against statistic interferences. On the other hand a complete digitalization of any and all signals as received and a search for individual amplitude maxima and subsequent evaluations thereof are too time consuming.